The present invention relates to positioning sensors with respect to substrates such as flat panel display glass substrates.
Processing of substrates, such as flat panel display (FPD) substrates, printed circuit boards (PCBs) or silicon wafers, involves subjecting substrates to various process conditions such as high temperatures, radio frequency (rf) plasma, chemical etching and ion bombardment. To produce good quality and high yield products, these process conditions must be maintained to a very high degree of uniformity across the surface of the substrate. Modem flat panel display substrates are large thin sheets of glass. Such large substrates make uniformity particularly difficult to maintain. In order to obtain good uniformity, process conditions must be measured to determine the variation across a substrate so that the variation may be reduced. For example, the temperature at different points on a substrate may need to be known in order to adjust process conditions to achieve better temperature uniformity. One way to measure such conditions is by using a substrate that has sensors attached to it.
Sensors may be mounted to a substrate to form an instrumented substrate that provides data on process conditions. Several sensors may be distributed on one or more surfaces of the substrate, or in recesses within the substrate, to create an array of sensors that monitors process conditions at various points. Such arrays of sensors are described by Renken et al., in U.S. Pat. No. 6,325,536, which patent is herein incorporated by reference in its entirety. Process conditions such as temperature, pressure, gas flow rates, chemical concentration, ion current density, position and acceleration may be monitored using such an array of sensors. Sensors may also be used for accurately measuring the physical location and orientation of a substrate.
Sensors may be placed in recesses in the surface of a substrate and cemented in place. This provides a strong attachment to the substrate. For example a temperature sensor may be embedded in this manner to ensure a strong attachment and good thermal contact with the substrate. Cement, or potting compound, may be used to retain the sensor in the recess and to provide good thermal contact with the substrate. Attaching a sensor in this manner is generally done in a dedicated facility by trained technicians. A substrate may be sent to such a facility by a customer to be instrumented in this manner. The recesses are created and the sensors embedded at the facility. Then, the instrumented substrate is sent back to the customer. For smaller substrates such as silicon wafers, an instrumented substrate may simply be shipped to a customer by regular mail or courier. However, FPD substrates are large and fragile and require special packaging and handling.
FPD substrates are rectangular with dimensions that may be greater than 2 meters. However, they are generally 1 millimeter thick or less. They are made of glass, which is brittle and is extremely fragile. This makes shipping difficult and expensive. Typically, a substrate is protected with impact resistant packaging material and is then enclosed within a shipping container such as a wooden crate. Even with such precautions, FPD substrates may be damaged in transit. After the substrate is instrumented with sensors at the facility and returned to the user, it is individually packaged with specially designed container. Transporting such large substrates may also be costly and time consuming, especially where international shipping is required.